Electric blasting cap



Aug. 1%44- A. B. MILLER ELECTRIC BLASTING CAP Filed Sept. 6, 1940 FiGrlABRAHAM B. MILLER INVENTOR.

contact with the explosive charge.

[ water. ,7

'tered in blasting operations, especially in deep Patented Aug. 22, 1944ELECTRIC BLASTING CAP Abraham B. Miller, Newark, DeL; Hazel E. Miller,

administratrix of said Abraham B. Miller,.deceased, assignor to HerculesPowder Company, Wilmington, DeL, a corporation of Delaware ApplicationSeptember 6, 1940, Serial No. 355,572 2 Claims. (01. 102-28) tractionand efiects a seal which provides a completely water proof assembly.

Heretofore in the manufacture of electric firing devices, for example,electric blasting caps, it has been the custom to cast a sulfur plugabout a pair of lead wires in a manner which provides a pair ofterminals adapted to be bridged with a high resistance bridge wire toform'suitable firing assemblies for example, a bridge plug, cavity typeplug or match head. The firing assemblies so formed have been insertedinto a cap shell containing an explosive charge at the closed endthereof so that the bridge wire is in initiating To position a bridgeplug or the like, the art normally introduces a waterproofingcomposition into the shell just above the, bridge plug which binds thebridge plug into place, and on top of this waterproofing compositionthere is introduced a sealing com- 1 position in order to moredefinitely seal the bridge plug into the shell.

The waterproofing materials used may be tar or asphalt or similarsticky. materials while the sealing compound is normally sulfur.

, The above type caps have not been entirely cially when the cap is usedunder a high head of High heads of water are often encounhold quarryblasting, in seismograph work and in oil well shooting. The blastingcaps sealed in accordance with the prior art often allowed wa-. ter toreach the explosive composition and cause desensitization thereof.

Further difiiculties have been encountered due to lack of storagequalities of the caps. Thus the tar or asphalt waterproofing mayduringstorage in hot weather find its way past the bridge plug ever thecapsare exposed to very cold temperatures because the tar or asphalthardens and 4 adhesion to shell walls is reduced to a point thatblasting cap which may be easily and efliciently sealed against alloutside influences.

A further object of this invention is to provide a bridge plug assemblywhich will act as an effective seal for a blasting cap shell.

A further object of this invention is to provide a method of sealingelectric blasting caps in a completel waterproof manner, A furtherobject of this invention is to provide a bridge plug which will permitthe construction of a shorter blasting cap.

A further object of this invention is to. provide a bridge plug assemblythat is not effected by changes in temperature.

A still further object of this invention is to provide a bridge plugassembly for electric blastingcaps which will expedite'mechanicalassembly.

Other and further objects oi this invention will appear hereinafter.

The objects of this invention are in general I accomplished by providingan elastic sleeve or coating between the blasting cap shell or casingcontaining an explosive charge and the bridge plug assembly which isplaced within the casing and in initiating contact with the explosivecharge therein. Thus, in accordance with the present invention there isprovided a bridge plug assembly comprising lead wires that are held indielectric relation with each other by a molded or cast plug composed ofan electrical insulating material, or the lead wires are insertedthrough apertures formed in a plug and firmly positioned will not resistany appreciable amount of water pressure.

The object of this invention is to provide a:

therein by suitable operations. The plug which holds .the lead wires inspaced relationship is formed to the proper diameter to fit within aloaded blasting cap shell. 'ing the molding, casting or formingoperations or after it is formed may be provided withgrooves about itsperiphery. Normally a plurality of grooves will be formed on the surfaceand the grooves will be so located that after insertion of the plug intothe blasting cap shell, the shell may be crimped into coactingrelationship with the grooves in a manner that providesan integralassembly. The crimping of the shell into the grooves, in itself howeverdoes not provide a seal that is completely waterproof and in accordancewith this invention the blasting cap is waterproofed by placing between.the bridge plug and the blasting cap shell a layer of elastic materialwhich preferably adheres tenaciously both to the plug and to the metalof the shell, This elastic material may be in the form of a preformedThe plug either dursleeve which is placed about the plug or it may be inthe form of a coating composition applied to the surface of the plugand/or to'the surface of the blasting cap. shell, or the two methods maybe combined, however, the elastic material fills any voids between theplug and the shell itself and effectively Waterproofs and seals theblasting cap assembly in a manner that provides a firing device that iscompletely waterproof.

-Having now indicated in a general way the nature and purpose of thisinvention, there follows a more detailed description of preferredembodiments thereof, with reference to the accompanying drawing in whichFig. 1 is a perspective view of a preformed bridge plug.

Fig. 2 is a perspective view of a sleeve of elastic material which isadapted to form the joint between the plug and the blasting cap shell.

Fig. 3 is a perspective view of the sleeve of Fig. 2 and the plug ofFig. 1 after they have been assembled for insertion into a blasting capshell. Fig. 4 is a completely assembled blasting cap shell.

Fig. 5 is a cross sectional view along line 5--5 of Fig. 4.

Referring now to the drawing there is shown a bridge plug assembly Iwhich comprises a pair of lead wires 2 held in a dielectric relationwith one another by a plug 3. The plug 3 may be molded, cast orotherwise'formed about the leg wire 2 or it may be formed per se and theleg wires 2 inserted therethrough. In either operation the leg wires areso positioned in the .plug that a, waterproof joint is obtained betweenthe wires and the material making up the plug.

The plug 8 may be prepared from materials such as sulfur, syntheticresin of the phenolaldehyde type either unfilled or filled;urea-aldehyde resin filled or unfilled; porcelain compositions;laminated paper; vulcanized fiber; Masonite; and other similardielectric materials which have electric blasting. cap is in order. Thisis accomplished by inserting into a loaded blasting cap shell 9 thebridge plug-elastic sleeveassembly I, positioning it in the properrelation to the shell and crimping the shell in a manner that forces theshell walls into the grooves 5 of the plug. The crimping operationadequately 'seals theblasting cap for use in all explosives operationsand forms a waterproof assembly which is especially desirable for use inexplosive operations where a high degree of water resistance isrequired.

proof assembly is obtained. Thus the elastic sleeve 6 forms a perfectjoint between the bridge plug 3 and the blasting cap shell 9.,

The elastic sleeve 6 shown in Fig. 2 may be fabricated as a tube adaptedto slip over the bridge plug or as a sheet adapted to be wrapped aboutthe plug and this sleeve or sheet may be of any desirable thickness, buta thickness of between about 0.005 and 0.0005 inchand preferably about0.001 inch has been found to be the best means ofobtaining a high waterresistant seal. In addition to the fabricated sleeve or sheet, the plugmay be coated by spraying or brushing or by meansof an ink pad. kissrollor the like with an elastic material. Elastic materials adaptable foruse as sleeves, sheets, or coatings in accordance with this inventionare for example rubber, gutta percha, chicle, balata, neoprene,"plasticized polyvinyl chloride and/or acetate, solutions or emulsions ofthese and other equivalent compounds or mixtures may be utilized forapplying the material to the plug or shell. I

Adherence between the plug shell and elastic material may be facilitatedby applying priming solutions of cementitious compounds in suitable theproper tensile strength and which may be bonded to the leg wires thatare to be inserted through the plug or which are to be surrounded by acast or molded plug.

The plug 3 has grooves 5 molded or formed into its periphery so that astrong mechanical ,bond may be formed between the blasting cap shell andthe bridge plug by crimping the shell into the grooves. For purposes ofillustration two grooves 5 are shown, however if desirable one or moregrooves may be formed on the surface or the grooves may'take the form ofspirals or definitely located indentations. These grooves, spirals orindentations are formed on the periphery of the plug 3 in a definitemanner so that it is possible to form similar grooves in the blastingcap shell in such a way that a positive mechanical bond is formedtherebetween.

After forming the bridge plug l comprising a pair of leg wires '2 and aplug 3, there is placed on the surface of the plug 3 a sleeve 6 (Fig. 2)so that an assembly I is produced. The assembly 1 comprises the bridgeplug of Fig. 1 with the sleeve of Fig. 2 slipped thereabout and is 111 lplroper form for insertion into a blasting cap s e wires- 2 electricallyconnected together by a highly resistant bridge wire 8 usually platinumor an alloy thereof. This, bridge wire 8 effects the detonation of theblasting cap, when an electric current is applied thereto.

Upon completing the assembly of the bridge plug and the elastic sleeve,the formation of the The bridge plug assembly has the leadsolvents tothe periphery of the plug and also if desired to the inner surface ofthe blasting cap shell. inserting the coated plug into the shell, andcrimping the two together. The adherence may be further increased bywarming the shell slightly before the crimping operation.

caps. Further, by avoiding the use of water-.

proofing, failures due to flowage during hot storage are prevented. Afurther advantage is a greatly increased water resistance of thefinished assembly and the much neater outside appearance of the capitself. Other advantages, will become apparent to those skilled in theart upon practicing this invention.

It will be understood that the details and examples herein before setforth as illustrative only, and that the invention as broadly describedand claimed is in no way limited thereby.

What I claim and Patent.is:. 1

1. An electric blastin i uhaving its component parts "prefabricatedand'adapted to mechanical assembly which comprises, a bridge plug ofdielectric material formed about a bridge Thus the desire to protect byLetters asmsa':

groove about its periphery, and a. relatively thin sleeve of aresilientmaterial interposed between said bridgeplug and a chargedshell, said charged pressed whereby the resilient properties thereofcompensate for l'liflferences in thermal expansivity betweenthe plug andshell to form a water 1 impervious cap.

2. The electric blasting cap according toiclaini shell crimped to-engagesaid groove in the bridge 5 1 wherein said sleeve. is preformed of a.robberplug, the elastic .vmaterial being highly ,com-

like resilient material. ABRAHAM B. MILLER.

